Hi Marcus and everyone,
Thank you for your feedback. Our artists have identified an with certain metal gloss/roughness maps, which are inverted. We are working on replacing all the effected maps and should be up and replaced shortly.
Regarding the PBR. We do not claim anywhere on the site that our library is full PBR, and it’s identified in our post as well. 
We have taken every step to remove as much lighting information as possible in our albedo maps. We really appreciate any type of feedback, but those are assumptions that cannot be made purely based off of our renders.
We’d love to see some examples of some of the rock textures that you felt are “plasticity” so we can look into and evaluate if there is a problem.
**UPDATE
We understand the concerns with the way we’ve presented the metals, and have decided to totally revamp the metal assets in a more appropriate way to address the concerns of the community.